Creates a clinician record for a user of your application. Set externalId to your own user identifier. Optionally pass roles (keys from GET /organizations/{organizationId}/clinician-roles); every clinician always holds clinician. Returns 409 if a clinician with this email already exists — search first with GET /clinics/{clinicId}/clinicians?email= if you are unsure — or if elevated roles are requested in an organization whose roles are managed by its identity provider.